If the CEL is not on and you get a code when you have the car scanned, that code is called an Intermittent code. The computer detected a problem, than, the CEL come on and then the problem went away and the CEL went off. The code stays in memory until it is cleared. I just got done scanning my minivan as it was idling rough even though the CEL did not come on. Turns out the air filter housing was not closed properly (iffy ube replaced the air filter for me previously). I put in a new filter, closed the housing properly, cleared the CEL and will drive for a few days to see if the idling improves and the CEL (or intermittent code) stays off. The scanner is one of the best investments for me. ($75 for a Actron 9125, $150 for 9135 or $250 for 9145- And auto parts stores occasionally have them on sale for another 20% or so discount).
